There are two phosphofructokinase (fructose 6-phosphate kinase) activities of Escherichia coli. Activity 1 is the main one in wild type strains (95%), and activity 2 appears in response to a suppressor. At least three genes govern the two activities. They may be products of different structural genes or, conceivably, different forms of the same enzyme. They have both been purified to homogeneity, and the anticipated work is to compare the two proteins: subunit structure, antigenicity, complementation, and, possibly, interconversion. BIBLIOGRAPHIC REFERENCES: Vinopal, R.T., and Fraenkel, D.G. 1975. The pfkB and pfkC loci of Escherichia coli. J. Bacteriol. 122: 1153-1161. Vinopal, R.T., Clifton, D., and Fraenkel, D.G. 1975. The pfkA locus of Escherichia coli. J. Bacteriol. 122: 1162-1171.